Laminated safety glass



Patented Jan. 30, 1940 v I UNlTED STATES PATENT OFFICE LAMINATED SAFETY GLASS Joseph D. Ryan and George B. Watkins, Toledo, Ohio, assignors to Libbey-Owens-Ford Glass Company, Toledo, Ohio, a corporation of Ohio No Drawing. Application June 13, 1934,

, Serial No. 730,464

7 Claims. (Cl. 49-92) The present invention relates to laminated hydrolysis, it was found that the resulting plastic safety glass and more particularly to laminated sheets were sufiiciently thermoplastic to permit safety glass involving the use of a cellulose aceto molding between two plates or sheets of glass in butyrate plastic sheet. customary laminating cycles wherein a pressure 5 Laminated safety glass is a composited strucof 200 lbs.- per square inch, and a temperature 5 ture composed of two sheets of glass and an of 300 F. for a period of five to ten minutes is interposed layer of tough, transparent plastic used. r material adherent tothe inner surfaces thereof. After developing. the plastic to this point,

In the early development of laminated safety namely, to a point where it is capable of being l0 glass, pyroxylin plastic was usually, if not always, molded under heat and pressure, it was found 10 used as the plastic layer. However, due to the ,that the plastic could not be readily bonded beinherent instability of pyroxylin plastic toward tween glass sheets. All attempts tobond the heat and light energy, with consequent fairly cellulose aceto butyrate plastic sheet to glass short life of laminated'safety glass made there.- surfaces using the well known adhesives for W with, it became evident that improved plastics bonding pyroxylin plastic and cellulose acetate 1-5 would have to be developed and the next stage plastics to sheets of glass failed to produce adwas probably the development of a process perhesion as did the application of various other mitting the use of cellulose acetate plastic. "materials such as, for example, natural and syn- Experience has shown that pyroxylin plastic thetic resins and various types and combinations 50 can be more readily bonded to glass than most of plasticizers commercially available.

other plastics, and one of the diflicult problems Our invention resides in the development and in the development of any improved plastics discoveryof abonding material suitable for bond- ,for use in the manufacture of laminated safety ing or giving excellent adhesion between the celglass resides in the simultaneous development lulose aceto butyrate plastic and glass surfaces.

5 of a bonding material which can be used to give The method we use in preparing the adhesive an adequate and satisfactory bond between said consists in subjecting the raw cellulose derivaplastic and glass laminations. tive (aceto butyrate of cellulose) to a rather Recently, a cellulose aceto butyrate plastic has severe chemical treatment, which treatment been developed which gives promise of being seems to completely change the nature of the l0 even more satisfactory than present day celcellulose derivative as regards its adhesive char 3 lulose acetate plastic. This cellulose aceto buty- 'acteristics to glass and yet the characteristics rate plastic might be termed in a general way thereof resembles the cellulose aceto butyrate a mixed esterof cellulose which is formed by plastic sufficiently to give compatibility or adesterifying cellulose with a mixture of acetic and hesion between the adhesive and the plastioized i5 butyric acids, thereby forming a triaceto butyrate sheet. 5 of cellulose or cellulose triaceto butyrate. Afterv subjecting the cellulose derivative to The characteristics of the cellulose triaceto chemical treatmentat elevated temperatures, the butyrate, with special reference to its high reresulting cellulosic residue is carefully purified, sistance to water absorption and a very low 00- dissolved and dispersed in proper solvents and emcientof thermal'plasticity, coupled with the plasticizers so that'it can be applied in thin films .40 fact that it can be plasticized, made such plastic to the glass surfaces by any of the well known prominent as a possible substitute for both means'such as spraying, film applying rolls, etc. pyroxylin plastic and cellulose acetate plastic. The cellulose aceto butyrate plastic sheet is However, we discovered that because of its then assembled'between the coated glass sheets, exceedingly low temperature coeflicient of plasthus forming a sandwich; and the laminations ticity, such plastic could not be properly embonded together by the'application of heat and ployed between two glass sheets using customary pressure. We have found a pressing cycle of methods of bonding glass-plastic laminations. 200'pound s per square inch at a temperature of The plastic was then further developed, par- 300 FLfor'aperiod of fromfive to ten minutes ticular attention being given to increasing its to be very effective in giving satisfactory bonding thermo plasticity, and accordingly the cellulose of the laminations.

triaceto butyrate was subjected to a partial hy- We have found'several different methods which drolysis similar to theprocess used formaking have proven, effective for chemically treating the acetone soluble cellulose acetate V from chloro-. raw aceto butyrate of cellulose in the manufacture 5 form soluble cellulose acetate. After this partial of the new adhesive.

The raw, partially hydrolyzed triaceto butyrate of cellulose is preferably converted into a finely sub-divided condition before being subjected to chemical treatment. This was found necessary due to the dense, horny-like character of the 300 grams of the raw sub-divided partially hydrolyzed triaceto butyrate of cellulose was suspended, with stirring, in 10 gallons of water and heated to 200 to 212 degrees F. Then 100grams of potassium permanganate was added and the mixture maintained just below the boiling point for about 3 hours. It has been noted that vigorous stirring of the reaction mixture is necessary for uniform results. At the end of the three hour period, the potassium permanganate is apparently completely reduced to manganate dioxide which must be removed, and this is preferably done by the use of reducing agents such as oxalic acid, sulfurous acid, etc., although it may be effected by a physical method with equally satisfactory results from the standpoint of the quality of adhesive produced. One physical method which was tried and found to give satisfaction involves filtering the reaction mass and drying. The reaction mass was then suspended in acetone (or other solvents) in which the manganese dioxide remains insoluble and then can be removed by filtration.

If the chemical method of removal of the suspended manganese dioxide is employed, after sufficient reducing agent has been added, the mixture in the reaction kettle is filtered, washed thoroughly, and dried.

An excellent adhesive for bonding the cellulose aceto butyrate plastic sheet to glass surfaces can then be made by dissolving the product of the chemical treatment in acetone or other suitable solvents to which may also be added plasticizers.

If a spray liquid is desired, the chemically treated product is dissolved in acetone or other volatile solvents to which also may be added plasticizers, for example, diethyl phthalate, dimethyl phthalate, triethyl citrate, etc. However, we have found that good adhesion is obtained even when the plasticizers are not included.

If an adhesive is desired which can be applied by a rolling method, then the chemically treated product is dissolved in mixtures preferably of medium boiling solvents such as monoethyl ether of ethylene glycol, acetate of the monoethyl ether of ethylene glycol, monoethyl ether of diethylene glycol, etc. as well as plasticizers.

It was found by a long series of experiments that the amount of oxidizing agent could be varied and satisfactory adhesives could be obtained. Like other chemical reactions, the treatment was found to be dependent upon the time, concentration of reactants, etc. other oxidizing agents, such as chromic acid, sodium dichromate in dilute acid solutions, potassium chlorate in dilute acid solutions, etc., were found satisfactory in carrying out chemical treatment.

Example N0. 2

300 grams of the raw, partially hydrolyzed triaceto butyrate of cellulose was suspended in two gallons of water and 125 c. c. of concentrated hydrochloric acid added. The mixture is then heated, with vigorous stirring, to the boiling point and maintained at this temperature for a period of about-4 hours. At the end of this time, the mixture is filtered and the chemically treated product washed free of acid with water and then dried.

The dried product can then be dissolved in the proper solvents as outlined in connection with Example (1) above, dependent upon whether a spray or roll liquid is desired.

The chemical treatment can also be carried out using either phosphoric acid, sulfuric acid, nitric acid, or mixtures thereof, and also salts of strong.

acids and weak bases or acid salts like sodium bisulfate.

Example N0. 3

300 grams of raw, partially hydrolyzed triaceto butyrate of cellulose is suspended in two gallons of 5% sodium hydroxide solution and the mixture heated to 200 F. for a period of two hours, at the end of which time the mixture is filtered, washed until free of alkali and then dried.

The dried product thus formed may then be dissolved in suitable solvents, either with or without plasticizers, and applied as an adhesive.

Other bases like potassium hydroxide, calcium hydroxide, and basic salts like sodium carbonate, can be used with equal satisfaction.

By way of example, it may be mentioned that an adhesive liquid particularly well adapted for application to the glass sheets by means of a roll film applying machine can be produced by mixing parts by weight of the chemically treated, partially hydrolyzed cellulose aceto butyrate, '75 parts by weight of the acetate of ethyl ether of diethylene glycol, 50 parts by weight of the acetate of ethyl ether of ethylene glycol, 50 parts by weight of the ethyl ether of ethylene glycol, and l5'parts by weight of dimethyl phthalate.

A suitable spray mixture can be made by mixing '70 parts by weight of the chemically treated, partially hydrolyzed aceto butyrate of cellulose, parts by weight of dimethyl phthalate, and sufficient acetone to give proper spraying consistency.

It will thus be seen that we have developed an adhesive for bonding cellulose aceto butyrate plastic to glass surfaces, which adhesive contains as the active ingredient percentages of the raw cellulose derivative having previously been chemically treated and then mixed with suitable solvents and plasticizers.

We claim:

1. Laminated safety glass comprising two sheets of glass and an interposed layer of tough, transparent, partially hydrolyzed cellulose mixed ester plastic, which in itself iacks adherence toward glass surfaces, bonded to said glass sheets with an adhesive formed from some of the same cellulose mixed ester as that comprising the plastic sheet and which has been further hydrolyzed to render it adherent toward glass surfaces.

2. Laminated safety glass comprising two sheets of glass and an interposed layer of tough, transparent, partially hydrolyzed cellulose mixed ester plastic, which in itself lacks adherence toward glass surfaces, bonded to said glass sheets with an adhesive formed from some of the same cellulose mixed ester as that comprising the plastic sheet and which has been further hydrolyzed and mixed with a plasticizer therefor.

3. Laminated safety glass comprising two sheets of glass and an interposed layer of tough, transparent, partially hydrolyzed cellulose aceto butyrate plastic bonded together with an adhesive formed from some of the same partially hydrolyzed cellulose aceto butyrate as that comprising the plastic layer and which has been further hydrolyzed.

4. Laminated safety glass comprising two sheets of glass and an interposed layer of tough, transparent, partially hydrolyzed cellulose aceto butyrate plastic bonded together with an adhesive formed from some of the same partially hydrolyzed cellulose aceto butyrate as that comprising the plastic layer and which has been further hydrolyzed and mixed with a plasticizer therefor.

5. Laminated safety glass comprising two sheets of glass and an interposed layer of tough,

transparent, partially hydrolyzed cellulose aceto prising the plastic layer and which has been,

further hydrolyzed to render it adherent toward glass surfaces while remaining compatible with said plastic layer.

6. The process of producing laminated safety glass comprising two sheets of glass and an interposed layer of tough, transparent, partially hydrolyzed cellulose mixed ester plastic lacking in adherence properties toward glass, including the steps of bonding said glass and plastic by means of an adhesive formed from some of the same cellulose mixed ester as that comprising the plastic layer and which has been further hydrolyzed to render it adherent toward glass surfaces under the combined action of heat and pressure.

'7. The process of producing laminated safety glass comprising two sheets of glass and an interposed layer of tough, transparent, partially hydrolyzed cellulose mixed ester plastic lacking in adherence properties toward glass,- consisting in bonding said glass and plastic by means of an adhesive formed from some of the same cellulose mixed ester as that comprising the plastic layer and which has been subjected toa treatment to further hydrolyze the same to render it adherent toward glass surfaces while remaining compatible with said plastic layer.

JOSEPH 1). RYAN. GEORGE B. WATKINS. 

